If you live in the South, a heat wave (or three) will occur each growing season. Of course, it’s a never-ending hot oven in some areas, but that can be exacerbated by periods of drought. Even in the Upper South, a higher-than-usual temperature and drought combo can be a death knell for gardens. As a long-time gardener, I do my best to prepare ahead for the high temperatures and water bills to come. Here’s what you need to do pre-, during, and post-heat waves to keep your garden healthy.
The Impact of Heat Waves on Gardens
Just like our bodies, heat waves cause problems for plants. The extremely high temperatures disrupt plant processes, including the development and growth of plant tissues, the reduction of nutrient uptake, photosynthesis rate, and pollen production, and damage to fruits and vegetables. Young and shallowly rooted plants are the most impacted by heat and drought, leaving them vulnerable to diseases and pests.
Beyond the expected wilting, plants’ leaves show heat stress by dropping, rolling, cupping, scorching, or scalding. You will see slow growth, fewer flowers or fruit as buds are “cooked,” and sunscald on fruit. While some plants will bounce back when fed and watered, others will not recover after severe heat stress.
Pre-Heat Wave Preparations
You know it’s coming, so be prepared for a heat wave. Check the weather forecast often to know when it will be the worst. Of course, these pre-wave preparations will not go to waste even if there is a “cool” Southern summer.
Water Deeply
When you water, water deeply to build up a plant’s water reserves. Lightly spraying water over a plant can cause it to have shallow roots that won’t hold up during the heat. Turn on a soaker hose for about 10 minutes, then turn the water off for an hour to allow the water to trickle down into the soil, not runoff. Then, turn the water back on. The moisture that has already been absorbed by the soil will pull the additional water down more quickly to the roots.
Add Mulch
Add mulch around plants and compost to the soil to help retain moisture. The mulch should be porous enough to let water and air pass through it, but dense enough to prevent weed growth. Wood chips, nut (pecan) shells, and pine straw are good mulch choices. Stay on top of weed control because they rob desirable plants of water and nutrients.
Avoid Overpruning Trees and Shrubs
Avoid overpruning trees and shrubs in early spring, as this can leave too much foliage exposed to sunscald. If you must prune heavily, do it before temperatures rise, as pruning can also cause plant stress.
Immediate Actions During a Heat WaveWater
When temperatures soar, watering is critical. It’s best to water early in the morning so that the soil is moist at least two inches deep, helping hydrate plants during the hottest part of the day. To provide water efficiently, spot water at the base of the plant, or use soaker hoses or drip irrigation systems. However, even though overhead watering, sprinkling, and misting can cause plant disease, during prolonged high temperatures, a humid environment probably outweighs the risk of plant disease.
Deadhead
Deadhead spent flowers to keep plants from expending energy on seed development. Deadheading helps prepare the plant to bloom again once the heat wave passes. Harvest vegetables as soon as you can to help the plant save energy. Do not fertilize plants during periods of extreme heat because the stimulated growth adds more stress to the plant. Try to wait until the heat wave breaks to apply pesticides which can burn leaves at high temperatures.
Use a Shade Cloth
Shade cloth is beneficial for heat-sensitive crops like peppers and tomatoes to reduce soil and air temperatures. Use stakes or cages to support a 30 percent shade cloth that doesn’t block too much light needed for healthy plants.
Consider Special Care for Containers
Container-grown plants are the most vulnerable during a heatwave. They may need to be placed in a shadier spot (under a patio umbrella or tree) during the hottest times of the day. Check them at least twice a day to make sure they have enough moisture in the soil. Remember that porous planters and hanging baskets will dry out more quickly than plastic or glazed pots.
Post-Heat Wave Recovery StrategiesWater Deeply
When temperatures break, continue to water deeply, covering an area wider than just under the plant so that all roots can absorb the needed moisture. Apply enough water to keep the soil moist at least two inches deep.
Remove Dead Flowers but Don’t Overprune
Remove dead flowers but leave any partially dead or scorched leaves in place. They are shading other foliage and if there is any green left on the leaf, it will continue to photosynthesis. Wait until cool weather to do any severe pruning. Remember, if you prune spring-blooming shrubs now, you’ll be cutting off buds that will be flowers next year.
Long-Term Strategies for Heat Resilience
You know the heat is coming, so select heat-loving plants and practice sustainable gardening year-round. You’ll only frustrate yourself and waste money by attempting to grow plants that aren’t suited to your climate. If you just can’t help yourself, plant “cool-growing” plants on the east and north sides of your garden; western and southern-facing beds are just too hot.
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Add these heat-tolerant plants to your garden for a better chance of surviving summer in the South:
Threadleaf coreopsis (Coreopsis verticillata)
Lion’s Ear (Leonotis leonurus)
Blanket flower (Gaillardia spp. and hybrids)
Butterfly Ginger (Hedychium coronarium)
Stonecrop (Hylotelephium spp.)
Black-eyed Susan (Rudbeckia hirta)
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